Examples of the technique of allowing a client to deposit data at a server and preventing information leak of the deposited data at the server in a server-client model include a search processing technique (refer to WO2012/077541) of performing, in accordance with a request from the client, a fast search of deposited encrypted data without decrypting the encrypted data nor performing a calculation with a heavy calculation load such as pairing.
This technique employs a probabilistic encryption method in which plaintext and encrypted text have a complicate one-to-m correspondence relation, the probabilistic encryption method being securer than a deterministic encryption method in which plaintext and encrypted text have a simple one-to-one correspondence relation. In this manner, the securer encryption method enables encrypted data to be searched without being decrypted, thereby preventing information leak from a server at which data is deposited, and allowing the server to securely search the deposited data.